I want know how many times people clicked on a particular button (should be very simple with Google analytics). However, I had an \"Uncaught ReferenceError: ga is not defined\"
The same problem occured in my Wordpress website. I had event tracking code in my contact form 7 additional field, but after I installed the plugin Monster Insights I had to delete the code in the Theme Options. Forgetting the code in my contact forms, I got this message too.
So delete all tracking code if you start using this plugin. Hope someone finds this information usefull..